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Realtime Library Functionssem_getvalue(3RT)


NAME

 sem_getvalue - get the value of a semaphore

SYNOPSIS

 
cc [ flag... ] file... -lrt [ library... ]
#include <semaphore.h>
int sem_getvalue(sem_t *sem, int *sval);

DESCRIPTION

 

The sem_getvalue() function updates the location referenced by the sval argument to have the value of the semaphore referenced by sem without affecting the state of the semaphore. The updated value represents an actual semaphore value that occurred at some unspecified time during the call, but it need not be the actual value of the semaphore when it is returned to the calling process.

If sem is locked, then the value returned by sem_getvalue() is either zero or a negative number whose absolute value represents the number of processes waiting for the semaphore at some unspecified time during the call.

The value set in sval may be 0 or positive. If sval is 0, there may be other processes (or LWPs or threads) waiting for the semaphore; if sval is positive, no processed is waiting.

RETURN VALUES

 

Upon successful completion, sem_getvalue() returns 0. Otherwise, it returns -1 and sets errno to indicate the error.

ERRORS

 

The sem_getvalue() function will fail if:

EINVAL
The sem argument does not refer to a valid semaphore.
ENOSYS
The sem_getvalue() function is not supported by the system.

ATTRIBUTES

 

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPEATTRIBUTE VALUE
MT-LevelMT-Safe

SEE ALSO

 

sem_post(3RT), sem_wait(3RT), attributes(5)


SunOS 5.9Go To TopLast Changed 22 Jun 1998

 
      
      
Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.